Question

我是C＃的新手。

请告诉我这段代码有什么问题。我使用两个输入字段EndValueTextBox和StartValueTextBox在数据库中插入数据。

我收到以下错误消息。 “对象引用未设置为对象的实例”

private void buttonSave_Click(object sender, EventArgs e)
{
    connection = new System.Data.SqlClient.SqlConnection();
     da = new SqlDataAdapter();
    try
    {
        connection.ConnectionString = "Data Source=.\\SQLEXPRESS;AttachDbFilename='G:\\C#.Net\\Forms Practice\\WindowsFormsPractice1\\WindowsFormsPractice1\\WindowsFormsPractice1.mdf';Integrated Security=True;Connect Timeout=30;User Instance=True";
    }
    catch (System.Exception ex)
    {
        MessageBox.Show(ex.Message,"Connection String");
    }
    try
    {
        connection.Open();
        string sql = "insert into TBLWORKERS (first_name , last_name )" + " values('" + StartValueTextBox.Text + "', '" + EndValueTextBox.Text + ")";
        //SqlDataAdapter da = new SqlDataAdapter(query, connString);


        da.InsertCommand.CommandText = sql;

        da.InsertCommand.ExecuteNonQuery();

    }
    catch (System.Exception ex)
    {
        MessageBox.Show(ex.Message, "Connection open");
    } 
}

Answer 1

您的SqlDataAdapter永远不会被分配连接来执行查询。您需要在施工期间或之后将SqlConnection与SqlDataAdapter相关联。

Answer 2

这一行da.InsertCommand.CommandText = sql;必须是这样的：

da.InsertCommand = new SqlCommand(sql);

Answer 3

string connetionString = "Data Source=.\\SQLEXPRESS;AttachDbFilename='G:\\C#.Net\\Forms Practice\\WindowsFormsPractice1\\WindowsFormsPractice1\\WindowsFormsPractice1.mdf';Integrated Security=True;Connect Timeout=30;User Instance=True";

SqlDataAdapter adapter = new SqlDataAdapter();

string sql =  "insert into TBLWORKERS (first_name , last_name )" + " values('" + StartValueTextBox.Text + "', '" + EndValueTextBox.Text + ")";

SqlConnection connection = new SqlConnection(connetionString);
try {
    connection.Open();
    adapter.InsertCommand = new SqlCommand(sql, connection);
    adapter.InsertCommand.ExecuteNonQuery();
} catch (Exception ex) {
    MessageBox.Show(ex.Message);
}

Answer 4

你什么时候例外？可能是那些行

System.Data.SqlClient.SqlConnection connection = new System.Data.SqlClient.SqlConnection();
SqlDataAdapter da = new SqlDataAdapter();

Answer 5

这是对您的代码（未经测试）的一个小重写，它应该处理没有分配连接对象的SqlDataAdapter，并演示如何使用参数化查询来帮助抵御SQL注入攻击：

private void buttonSave_Click(object sender, EventArgs e)
{

    try
    {
        // The using block will automatically dispose of your connection when
        // the block is exited and is considered standard practice.
        using (SqlConnection connection = new SqlConnection("Data Source=.\\SQLEXPRESS;AttachDbFilename='G:\\C#.Net\\Forms Practice\\WindowsFormsPractice1\\WindowsFormsPractice1\\WindowsFormsPractice1.mdf';Integrated Security=True;Connect Timeout=30;User Instance=True";))
        {

            SqlDataAdpter da = new SqlDataAdapter();

            connection.Open();

            // Assign the SqlConnection object to the SqlDataAdapter
            da.Connection = connection;

            // Parameterize the query as shown below
            string sql = "INSERT INTO TBLWORKERS(first_name, last_name) VALUES(@first_name, @last_name)";

            da.InsertCommand.CommandText = sql;

            // Add the values for the parameters
            da.InsertCommand.Parameters.Add("@first_name", SqlDbType.NVarChar, 25, StartValueTextBox.Text);
            da.InsertCommand.Parameters.Add("@last_name", SqlDbType.NVarChar, 25, EndValueTextBox.Text);

            // Execute the query - rows will have the number of rows
            // affected.  should be 1 in this case if succesful
            int rows = da.InsertCommand.ExecuteNonQuery();           
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message, "Connection open");
    }
}

你调用的对象是空的。请帮助解决错误

5 个答案: